Method of reinforcing corrugated paperboard

ABSTRACT

TRANSVERSELY OF THE FLUTES WHILE THE THERMOPLASTIC MATERIAL IS SOFT, AND MADE INTO CONTAINER BLANKS.   THIS INVENTION RELATES TO A METHOD OF REINFORCEING CORRUGATED PAPERBOARD. SINGLE FACE CORRUGATED PAPERBOARD IS FORMED, AND THEN ELONGATED STRIPS OF THERMOPLASTIC MATERIAL ARE DROPPED INTO THE VALLEYS FORMED BETWEEN THE CORRUGATIONS AT SPACED INTERVALS. THE SECOND LINER IS ADHERED TO THE CORRUGATED MEDIUM TO ENCLOSE THE STRIPS. THE DOUBLE FACE CORRUGATED BOARD IS HEATED TO DRY THE ADHESIVE AND RENDER THE REINFORCING STRIPS TACKY TO ADHERE TO THE CORRUGATED MEDIUM. THE CORRUGATED MAY THEN BE CREASED

June 22, 1971 J. c. BRACKETT 3,586,564

METHOD OF REINFORCING CORRUGATED PAPERBOARD Original Filed Oct. 24, 1965 2 Sheets-Sheet 1 INVENTOR Jon/v C. BRACKET! ATTORNEY June 22, 1971 J. c. BRACKETT 3,586,564

v METHOD OF REINFORCING CORRUGATED PAPERBOARD Original Filed Oct. 24, 1965 2 Sheets-Sheet 2 INVENTUR JOHN C. BRACKET? ATTORNEY United States Patent Office 3,586,564 Patented June 22., 1971 3,586,564 METHOD OF REINFORCING CORRUGATED PAPERBOARD John C. Brackett, St. Paul, Minn., assignor to Hoerner Waldorf Corporation, Ramsey County, Minn. Original application Oct. 24, 1965, Ser. No. 504,575, now Patent No. 3,411,689, dated Nov. 19, 1968. Divided and this application Sept. 10, 1968, Ser. No. 758,748 Int. Cl. B31f 1/20 US. Cl. 156-210 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of reinforcing corrugated paperboard. Single face corrugated paperboard is formed, and then elongated strips of thermoplastic material are dropped into the valleys formed between the corrugations at spaced intervals. The second liner is adhered to the corrugated medium to enclose the strips. The double face corrugated board is heated to dry the adhesive and render the reinforcing strips tacky to adhere to the corrugated medium. The corrugated may then be creased transversely of the flutes while the thermoplastic material is soft, and made into container blanks.

This application is a division of application Ser. No. 504,575, filed Oct. 24, 1965, now U.S. Pat. No. 3,411,- 689.

This invention relates to an improvement in reinforced corrugated paperboard and to a method of making the same. I

Reinforced corrugated paperboard is oftentimes used for containing products which are heavy, and yet which are incapable of withstanding compressive force, and as a result the containers tend to bulge when they are stacked one upon another. An object of the present invention resides in providing a means of stiffening corrugated paperboard so that it is capable of withstanding greater compressive force.

Certain types of plastic are capable of withstanding considerable compressive force, particularly when held from bending. I have found that by forming narrow strips of such plastic, and dropping them into the flutes of the corrugated board at intervals, the board formed is materially stiffened. This is particularly true if the plastic is of a type which softens with heat and is capable of bonding two of the corrugated mediums when subjected to heat.

In the formation of double-faced corrugated board which includes a corrugated medium sandwiched between a pair of paper liners, the combined web is normally directed over a series of heating plates to dry the adhesive. These plates are normally heated to a high temperature by steam under pressure. I found that if narrow strips of plastic are fed between the flutes of the corrugated medium before the medium is attached to the second liner, the plastic may bond to the medium as the web passes over the heating plates. As a result, certain of the flutes of the corrugated board are partially filled with plastic, which is held firmly in place by being bonded to the paperboard. The resulting corrugated board is much stiffer than normal corrugated board in a direction parallel to the flutes. At the same time, the paperboard may be creased in the usual manner to form corrugated containers.

Corrugated container blanks are usually formed with the corrugations extending vertically with the fold lines connecting the side walls of the container to the closure flaps extending transversely of the corrugations. These two fold lines are normally formed on the corrugations and while the paperboard is still in a heated condition from the heating plates. As a result, the creases which extend transversely of the reinforcing strips are applied while the plastic is still warm and in a pliable condition, simplifying the creasing operation.

These and other objects and novel features of the present invention will be more clearly and fully set forth in the following specification and claims.

In the drawings forming a part of the specification,

FIG. 1 diagrammatically illustrates the starting end of a corrugating apparatus showing the manner in which single face corrugated is produced.

FIG. 2 is, in effect, a continuation of FIG. 1 showing the manner in which the single face corrugated is combined with the second liner and diagrammatically illustrates a cutter for forming narrow strips of plastic to be incorporated in the paperboard.

FIG. 3 shows the manner in which the corrugated strips are dropped in to the flutes of the corrugated board.

FIG. 4 is a sectional view, in exaggerated size, showing the finished corrugated board.

FIG. 5 is a perspective view showing a container formed of the corrugated board.

The drawings show diagrammatically an apparatus for forming corrugated paperboard. The apparatus differs from conventional apparatus only in the fact that the second liner is adhered to the upper surface of the single face corrugated web rather than to the undersurface thereof to facilitate the feeding of the thermoplastic material between the flutes of the single face corrugated board. Con ventional equipment may be used if a different means of positioning the thermoplastic material in the flutes is employed.

In the arrangement illustrated, the numeral 9 indicates the roll of corrugating medium the web 10' from which is directed between a pair of corrugated rolls 11. Adhesive is applied to the flutes of the corrugated medium as indicated at 12. A roll of liner 13 is pivotally supported as indicated at 14, and the liner 15 is guided by suitable rollers 16 around a pressure roll 17 which applies the liner 15 to the corrugated medium 10. The single face corrugated web thus formed is then normally festooned upon a conveyor 19 where the adhesive is allowed to partially dry.

As indicated in FIG. 2 of the drawings, the single face corrugated web 20 is directed by guide rollers such as 21 beneath a cutter unit 22 which cuts olf narrow strips 26 of thermoplastic from a web 23 which may be fed from a roll 24 pivotally supported at 25. The narrow strips 26 of thermoplastic material are dropped upon the surface of the single face corrugated web 20 and means 27 are provided for straightening the strips 26 and insuring their entry into one of the flutes of the corrugated medium. Ad hesive is applied to the flutes of the single face corrugated web 20 by an adhesive applicator 29. A second web of liner 30 is fed from a roll 31 pivotally supported at 32, and the web 30 is adhered to the surface of the flutes of the corrugated medium. The corrugated web thus formed is heated by passing over a series of heating plates 33 which are normally heated to a high temperature by steam under pressure.

FIG. 3 of the drawings discloses in greatly enlarged form the thermoplastic strips 26 lying in certain of the flutes of the corrugated web. The spacing between the strips determines, to some extent, the amount of reinforcing obtained. As the web of the corrugated paperboard passes over the plates 33, the thermoplastic is heated to the extent necessary to soften it, and to cause it to bond to the corrugated medium. If the thermoplastic strips are applied on the conventional apparatus, the thermoplastic may bond to the bottom liner as well as, or instead of, the corrugated medium. In any event, the thermoplastic strips are bonded in position.

The corrugated web is normally cut into sheets at the end of the corrugating apparatus and the web is usually creased if the sheets are to be used to form corrugated containers; When removed from the corrugator, the sheets are normally at an elevated temperature. While the sheets can be readily handled, they are at a temperature which is substantially higher than room temperature. Thus the thermoplastic material is still in a relatively soft condition at the time the web passes between the creasing rollers, thereby facilitating thecreasing operation.

The length of the strips of thermoplastic material may be varied. For example, where the strips are to reinforce the corrugated board to provide additional stacking strength, it is only necessary that the strips be of sutficient length to extend between the crease line connecting the walls of the container to the closing flaps. FIG. of the drawings shows a conventional container A having side walls such as 35 and opposed end walls such as 36. The Walls are provided with closure flaps, two of which are indicated at 37. The reinforcing strips 26 are shown in dotted outline extending vertically of the side and end walls as well as across the closure flaps.

I have described the principles of construction and peration of my improvement in reinforced corrugated paperboard and the method of making the same; while I have endeavored to set forth the best embodiment thereof, I desire to have it understood that obvious changes may be made within the scope of the following claims without departing from the spirit of my invention.

What is claimed is:

1. A method of forming a reinforced corrugated paperboard web including the steps of forming a corrugated medium from a web of flat paperboard, the corrugations extending transversely of the web,

adhering a web of liner to a surface of the corrugated medium to form single face corrugated board, dropping strips of thermoplastic material between the flutes of the corrugated medium at spaced intervals, the strips being positioned between and partially filling the space between pairs of adjoining flutes, arranging the strips so as to lie entirely below the crests of the adjoining flutes, adhering a second web of liner to the corrugated medium on the side opposite that to which the first liner was adhered,

heating the web thus formed to bond the thermoplastic strips in position to the corrugated medium and to dry the adhesive and cooling the web below the softening point of the thermoplastic material.

2. The method of claim 1 and including the further step of creasing the web transversely of the corrugations while the web is at an elevated temperature.

3. The method of claim 1 and including the further step of cutting the web longitudinally of the corrugation to form creased sheets.

4. The method of claim 3 and including the further step of slotting and creasing the sheets parallel to the corrugations to form a container blank.

5. A method of forming a reinforced corrugated paperboard web including the steps of forming a corrugated medium from a web of paperboard, the corrugations extending transversely of the web, adhering a web of liner to a surface of the corrugated medium,applying strips of thermoplastic material parallel to said corrugations and between the flutes of the corrugated medium at spaced intervals, adhering a second Web of liner to the corrugated medium on the side opposite that to which the first liner was adhered, heating the web thus formed to bond the thermoplastic material in position and to dry the adhesive, and cutting the strips of thermoplastic material from a web of such material.

6. The method of forming a reinforced corrugated paperboard web including the steps of forming a corrugated medium from a web of paperboard, the corrugations extending transversely of the web, adhering a web of liner to a surface of the corrugated medium, feeding a web of thermoplastic material adjacent to the corrugated medium, cutting strips of thermoplastic material from said web of thermoplastic material and applying the strips between the flutes of the corrugated medium at intervals, and heating the web to dry the adhesive and to bond the thermoplastic strips to position.

7. The method of claim 6 and including the strip of adhering a second web of liner to the corrugated medium on the side thereof opposite that to which the first liner was adhered prior to heating the web.

References Cited UNITED STATES PATENTS 1,780,739 11/1930 Berg 156-210X 1,914,845 6/1933 Cook 229-3.5X 2,983,636 5/1961 Runton 156210 3,033,723 5/1962 Mead 156-292X 3,307,994 3/1967 Scott, Jr. 156-21O SAMUEL W. ENGLE, Primary Examiner US. Cl. X.R. 

